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Infrared switch circuit schematic presentation

2015-09-27 23:07  
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This article describes an infrared switch circuit schematic presentation. The principle is simple there, we recommend that combine text carefully read the complete schematic. This is a single-channel (ON / OFF) universal switch, may be used in any infrared remote control with 36-38kHz. Figure: IC1 is an infrared module. IR modulated pulses received and buffered through this IC. It has a standard TTL output, no signal is raised high by R1. A gate of a CMOS inverter drives LED1 as a visible switching aid. Another gate signal is applied to the time constant of the buffer circuit, comprising R3, R4 and D1, C2. C2 charges through R3, R4, D1, and the discharge by preventing the rapid discharge through the low output impedance of the CMOS buffers. The time charging capacitors resistors and capacitors, commonly known as the RC time constant. In an RC capacitor will only be charged 63% of the supply voltage. It requires a capacitor 5 RC 99% of the cost. In this circuit, charging of the capacitor must meet the logic threshold of the CMOS inverter. As power supply is a 5 volt, the input threshold is about 3.6 v, which requires approximately 3 rc of about 1.5 seconds. Once you reach the inventor trigger 555 timer and operating triggers. An analog pulse is received, filtered, and the output pulse as shown.

.IR Switch


IR pulses

The pulses are further buffered and contain “jaggered edges” as shown above. These edges are produced by the modulated IR data, and have to be removed. This is achieved using a 555 timer wired as a monostable, IC3, having an output pulse duration R5, C4. A clean output pulse is produced to activate the bistable latch, IC4. This is a D type flip flop, built with a TTL 7474 series IC and configured as a bistable. Any version of the 7474 may be used, i.e. schottky 74LS74, high speed  74HCT74  etc. The input is applied to the clock pin, the inverted output fed back to the data input and clear and preset lines are tied to ground. For every pulse the relay will operate and latch, the next pulse will turn off the relay and so on. Note that quick turn on and off of the relay is not possible. The output pulse is set at about 2.4 seconds. and input delay by R3, C2 set about 1.5 seconds.

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Parts List:
R1 3k3
R2 1k
R3 22k
R4 220k
R5 1M
R6 3k3
B1 12 V
D1 1N4148
D2 1N4003
Q1 B109
IC1 IR1 available from Harrison Electronics or TSOP1838 or similar
IC2 4049
IC3 CA555
IC4 SN74HCT74 or SN74LS74
IC5 LM7805
Relay 12 Volt coil with changeover contact
C1 100u
C2 22u
C3 100n
C4 2u2

VN:F [1.6.9_936]


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